High performance electronic equipment such as computers and particularly the processor portion of a computer must be shielded from radio frequency interference and from electromagnetic interference in order to reliably operate. Electromagnetic interference/radio frequency interference (EMI/RFI) interferes with the signals on the different lines leading to and from the computer and within the computer processor itself, since the lines leading to and from the computer act as antennas and an electrical current may be generated in those electrical conductors as a result of being a receiver for EMI/RFI.
In order to protect the electronic device, from the EMI/RFI and to improve its performance, the electronic device is typically enclosed within a metal cabinet which in turn is grounded. The metal cabinet acts as a receiver for the EMI/RFI and the resulting signals generated in the cabinet are then grounded and thereby prevented from effecting the reliable and efficient operation of the electronic system contained therein.
Additionally, the electronics of the electronic system generate EMI/RFI interference. There exists requirements for an EMI/RFI generating device to be equipped with shielding to prevent the propagation of such interference.
Typically, cabinets are a self-contained item having five sides including a bottom, three sides and a top and additionally a door or closure attached on the open side. The top and bottom may contain a perforated sheet to allow for air flow in and out of the cabinet. The cabinet may have a door or closure adjacent to each other, on opposite sides or wherever access is needed to the cabinet.
In order to prevent leakage, either incoming or outgoing, of EMI/RFI through the gap between the cabinet enclosure and the door, many attempts have been made to conductively connect the door and the cabinet and at the same time seal the gap between the two metal pieces. In order to effectively shield the contents of the cabinet from EMI/RFI, the door, in addition to being connected through the hinges, must be efficiently connected electrically to the cabinet itself around the opening to the cabinet. When a large system computer cabinet frame is assembled, for example, it is painted with a conductive paint to provide a conductive path to ground and also to provide corrosion protection.
Tin plated copper strips with a silver filled conductive pressure sensitive adhesive and a protective strip that may be removed from the adhesive to allow its installation are commercially available. These strips are applied over the bare metal of the frame, typically before, painting. The conductive pressure sensitive adhesive material carried by the tin/copper strips relief upon silver fill material in the conductive pressure sensitive adhesive for conductivity between the frame and the tin plated copper strip. The conductivity of the adhesive can vary with the amount of pressure applied to the adhesive during application.
The cost of this material is exceptionally high due to the silver content. The strip is typically applied to the bare metal of the frame and positioned around the periphery of the opening to the cabinet such that when the door of the cabinet closes and a resilient electrically conductive gasket material carried by the door is engaged in face-to-face contact with the tin plated copper strip, the electrical path between the door through the electrically conductive gasket, the tin plated copper foil and the conductive pressure sensitive adhesive is completed to the bare metal of the frame.
An example of such an electrically conductive tape is found in the IBM Technical Disclosure Bulletin, Vol. 14, No. 2, July, 1971; page 474.
A further example of efforts to address the problem of electromagnetic compatibility, i.e., shielding for EMI, is described and disclosed in the IBM Technical Disclosure Bulletin, Vol. 14, No. 2, July, 1971, page 518.
U.S. Pat. No. 4,977,296 to Hemming, discloses a metal foil with adhesive strips placed parallel to each other along the surface of the metal foil thus causing a ridge/valley contour forming a multiplicity of small wave guides which are effective in attenuating electromagnetic energy by virtue of their physical characteristics. The shielding tape disclosed by
Hemming is utilized to join together adjacent panels of shielding material which have been positioned on a fixed wall or structure.
It is an aspect of this invention to be able to establish electrical continuity between the closure of an electronic systems cabinet and the electronic systems cabinet itself.
It is a further aspect of the invention that the continuity between the closure and the frame of the cabinet is not dependent upon a conductive adhesive material, but rather upon highly conductive metal foils.